Past exam of the mathematics course of the University of Cambridge / 2006 / ia / Paper 5 / 2 (Operating Systems)

False. The Windows XP Executive implements core object management, memory management, process management and input-output services in privileged mode, as part of the kernel image. User applications and environment subsystems invoke these services through controlled entry points; they do not turn the Executive into user-mode code. This distinction is explicit in Microsoft's description of the Executive layer.

False. An access matrix is an authorization table, not a numerical matrix representing a linear transformation. Its entries are sets of rights, such as permission to read or write an object. “Inverting” its organization means obtaining subject-oriented capability lists from object-oriented access control lists, or conversely, by enumerating and regrouping entries. Numerical floating-point matrix inversion has neither the relevant operations nor the relevant semantics, and many access tables are not even square.

True. In polled input-output, a processor reads device status and handles ready work without interrupt entry and return overhead. If an operation completes very quickly, or requests arrive continuously at a high rate, a short poll or a batch of polls can cost less than an interrupt for every event. Interrupt-driven input-output is usually better for long or infrequent waits because the processor can do unrelated work or sleep instead of busy waiting. The useful choice depends on the event rate and latency requirement.

False as a general performance claim. A microkernel moves services into separate protection domains, which can require extra messages, scheduling and address-space transitions. A monolithic kernel can often call a service directly within its own privileged address space. The microkernel gains isolation and modularity, but these do not imply greater speed. Efficient implementations and particular workloads can change the comparison; the architecture alone gives no universal ordering.

True in the intended comparison with traditional Unix protection mechanisms. Windows XP provides object-specific access control lists, subject tokens containing identities and privileges, and a security reference monitor. Rights can distinguish operations on files, registry keys, processes and other protected objects. Traditional Unix file permissions distinguish read, write and execute for owner, group and everyone else; unrestricted root authority also makes privilege separation coarse. The richer Windows XP mechanisms can express finer least-privilege policies. Cambridge's access-control notes describe this architectural contrast.

This is an architectural capability comparison, not a claim that every Windows XP installation resists attacks better than every Unix installation. More complex authorization is not itself a proof of security; configuration and implementation matter, and Unix variants can add access control lists and other protection mechanisms. Without specifying that traditional model, the blanket comparison is underspecified.